Electrical device



March 9, 1937. A. 'r. WITTS ELECTRICAL DEVICE Filed July 5, 1953 Q dE;

INVENTOR Alf 50 77/ 4/45 WIT/5 ATTORNEY Patented Mar. 9, 1937 UNITED STATES mcrnrcar. nsvros Alfred Witts, Surrey, England, anlsnor Thomas to Radio Corporation of America, a corporation of Delaware Application July 5, 1988, Serial No. 879,050 In Great Britain Ill]! 22, M32

GCIa-ima.

This invention relates to electrical overload, safety, alarm and like devices and has for its object to provide a sensitive arrangement whereby safety means such as switches, will be opers ated and/or alarm devices such as indicators or bells will be actuamd if the current in a pare ticular circuit increases a predetermined amount above or decreases a predetermined amount below a predetermined value. The invention is particularly adapted for use in connection with the actuation of safety or alarm devices for protecting against or giving warning of predetermined increases or decreases in current in the anode circuit of a thermionic valve employed for example in a thermionic valve radio transmitter. The

invention is, however, not limited to this application.

It is customary in thermionic valve transmitters to provide overload devices, but such devices are m for practical reasons usually set to operate only when substantial increases in current occur and it is advisable therefore to provide a more sensitive device which will give an indication for quite a small increase (or in some cases decrease) of anode current. The present invention may be with advantage employed for this purpose.

According to this invention a resistance which forms part of a so-called electric discharge tube "blink" circuit is associated also with the circuit to be protected and frequency responsive means are arranged to be actuated by the frequency of the said blink circuit, the whole'arrangement being" such that when the current in the circuit to be protected reaches a predetermined value, the frequency in the "blink" circuit will be such as to actuate the frequency sensitivemeans.

The invention is illustrated in the accompanying drawing which shows diagrammatically one arrangement in accordance therewith and 40 adapted to give warning of an increase of current in the anode circuit of a thermionic valve transmitter.

Referring to the drawing V is the valve in question and, as will be seen, there is included in the anode circuit thereof and in series with,

* the anode cathode path thereof a resistance R1 which also forms part of a neon .tube "blink" circuit, the said neon tube "blink circuit including in a series loop the said resistance R1 a second resistance R: which is preferably adjustable, an ironcored inductance member L, a neon lamp or other electric discharge lamp N and a source of potential P.

The neon lamp is shunted by a condenser C which is preferably adjustable. The circuit conthe source of potential P the iron cored inductance L and the two resistances R1 and R: of

course constitutes a so-called blink circuit and pulsations of current will flow therein at a a frequency predetermined by the resistance, capacity, and E. M. F. in the said circuit. In the leakage field of the'iron cored inductance is arranged a resonant reed RR and the said reed and the various components of the "blink cir- 10 cuit are so adjusted hat so long as the current in the anode circuit of the valve does not exceed a predetermined value, the voltage drop across the resistance in said anode circuit is such that the frequency of the blink circuit is too high to is actuate the reed. If, however, a predetermined 3 increase in anode current occurs, the voltage applied to the neon tube will decrease due to the increased voltage drop across the resistance which is common both to the blink" circuit and the go anode circuit, and in consequence, the frequency of the "blink" circuit will fall to a value bringing it into resonance with the natural frequency of the reed. Accordingly. the reed will vibrate and this vibration may be utilized in any convenient -way (not illustrated); for example, it may serve to give a visible indication or it may actuate an audible or visible warning device, or it may actuate a safety device as may be deemed desirable. If desired, two reeds of different natural fre- 3o quencies may be associated with the iron cored inductance one having a resonant frequency above, and the other a resonant frequency below the frequency obtained in the "blink circuit when the. anode current is at a correct value. 35

, Thus, an'inc'rease or a decrease in anode current will result in the actuation of one or the other reed.

As above stated, the invention is primarily designed and intended for the actuation of warn- 4o ing devices, the apparatus being intended to give an indication to the engineer in charge as soon as a fault is developing, in order that he may ascertain and clear the fault before the normally provided less sensitive overload device comes into 5 operation.

Having now particularly described and ascertained the nature of my said invention'and in what manner the same is to be performed. I

declare that what I claim is: o

1. An electrical overload, safety alarm and like device adapted to be operated when the current in a circuit to be protected increases or decreases by a predetermined amount from a predetermined value, said device comprising a reas 2.,An electrical overload, safety, alarm or like device adapted to be operated when the'current in a circuit to be protected increases or de- 15 creases by a predetermined amount from a predetermined value, said device comprising a resistance in series in said circuit, a loop circuit including a source of potential, an inductance and a neon or similar electric discharge lamp in 20 series with said resistance, a condenser in shunt with said discharge lamp, andfrequency sensitive means connected with said condenser and discharge tube so as to actuate the alarm and to be actuated by energy derived from said series "loop circuit, the component elements, of said series loop circuit being of such magnitude that frequency of blink set up therein is substantially the same as that of the frequency sensitive means when the current through the resist- 9 ance reaches a predetermined value at which the device is intended to operate. 7 3. An electrical overload safety alarm device to operate when the current in a circuit to be protected exceeds or decreases by a predeter- 5 mined amount from a predetermined value, said device comprising a resistance in series with a circuit to be protected, a loop circuit including a source of potential, an inductance in the form of a choke coil connected in series with a second 4 resistance, an electrical discharge lamp in series with said choke coil and resistances, a condenser in shunt with said dischargelamp, frequency sensitive means comprising a vibratory reed actuated by the leakage field of said choke 4 coil and connected with said condenser and discharge tube so as to actuate an alarm by energy derived from said loop circuit when the frequency set up therein is substantially the same as the frequency sensitive means when the current through said resistance reaches a predetermined value at which said device is intended to operate.

4. An electrical overload safety alarm device to operate when the current in a circuit to be protected exceeds or decreases by a predetermined amount from a predetermined value, said device comprising a resistance in series with a circuit to be'protected, a loop circuit including a variable resistance, an iron choke coil, a source 7 energy derived from said loop circuit when the frequency set up therein is substantially the same as the frequency sensitive means when the current through said resistance reaches a predetermined value at which said device is intended to operate.

5. An electrical overload safety alarm device to operate when the current in a circuit to be protected exceeds or decreases by a predetermined amount from a predetermined value, said device comprising a resistance in series with a circuit-to be protected, 2. loop circuit including a source of potential, an inductance in the form of a coil capable of producing a leakage field, an electrical discharge lamp in series with said coil and resistance, a variable condenser in shunt with said discharge lamp, frequency sensitive means comprising a vibratory reed actuated by the leakage field of said choke coil and connected with said condenser and discharge tube so as to actuate an alarm by energy derived from said loop circuit when the frequency set up therein is substantially the same as the frequency sensitive means when the current through said resistance reaches a predetermined value at which said device is intended to operate.

6. An electrical overload safety alarm device to operate when the current in a circuit to be protected exceeds or decreases by a predetermined amount from a predetermined value, said device comprising a resistance in series with a circuit to be protected, a loop circuit including a source of potential, an inductance member capable of producing a leakage field, an electrical discharge lamp in series with said inductance and resistance, a condenser in shunt with said discharge lamp, frequency sensitive means comprising two vibratory reeds, one of said reeds being above, and the other being below the frequency set up in said circuit to be protected, said reeds actuated by the leakage field of said inductance member and connected with said condenser and discharge tube so as to actuate an alarm by energy derived from said loop circuit when the frequency set up in said loop circuit corresponds to the frequency of either one of said reeds.

ALFRED THOMAS WITTS. 

